Spectropolarimetry of Core-Collapse Supernovae

TL;DR

Spectropolarimetry reveals that core-collapse supernovae are generally aspherical, with the degree of asphericity linked to the progenitor's hydrogen envelope mass, indicating asymmetric explosion mechanisms.

Contribution

This paper reviews the use of spectropolarimetry to study supernova geometry and highlights the correlation between envelope loss and increased asphericity in core-collapse supernovae.

Findings

Asphericity is common in young core-collapse supernovae.

Progenitors with larger hydrogen envelopes show lower polarization.

Greater asphericity is observed in supernovae with lost or absent hydrogen/helium layers.

Abstract

We briefly review the young field of spectropolarimetry of core-collapse supernovae (SNe). Spectropolarimetry provides the only direct known probe of early-time supernova (SN) geometry. The fundamental result is that asphericity is a ubiquitous feature of young core-collapse SNe. However, the nature and degree of the asphericity vary considerably. The best predictor of core-collapse SN polarization seems to be the mass of the hydrogen envelope that is intact at the time of the explosion: those SNe that arise from progenitors with large, intact envelopes (e.g., Type II-plateau) have very low polarization, while those that result from progenitors that have lost part (SN IIb, SN IIn) or all (SN Ib) of their hydrogen (or even helium; SN Ic) layers prior to the explosion tend to show substantial polarization. Thus, the deeper we probe into core-collapse events, the greater the asphericity seems to be, suggesting a fundamentally asymmetric explosion with the asymmetry damped by the addition of envelope material.